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A265200 Numbers n such that n!3 + 3^7 is prime, where n!3 = n!!! is a triple factorial number (A007661). 3
8, 10, 11, 13, 16, 19, 20, 22, 37, 38, 47, 73, 92, 94, 100, 218, 241, 284, 482, 541, 736, 787, 829, 916, 1147, 1312, 1856, 1928, 2035, 3134, 4958, 5503, 8042, 16898, 16987, 24548, 25076, 35086 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding primes are: 2267, 2467, 3067, 5827, 60427, 1108747, 4190987, 24346507, 664565853954187, ...

a(39) > 50000.

Terms > 38 correspond to probable primes.

LINKS

Table of n, a(n) for n=1..38.

Henri & Renaud Lifchitz, PRP Records. Search for n!3+2187.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

EXAMPLE

11!3 + 3^7 = 11*8*5*2 + 2187 = 3067 is prime, so 11 is in the sequence.

MATHEMATICA

MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];

Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 3] + 3^7] &]

PROG

(PARI) tf(n) = prod(i=0, (n-1)\3, n-3*i);

for(n=1, 1e4, if(ispseudoprime(tf(n) + 3^7), print1(n , ", "))) \\ Altug Alkan, Dec 04 2015

CROSSREFS

Cf. A007661, A037082, A084438, A123910, A242994, A261145.

Sequence in context: A242857 A031037 A006757 * A126803 A256385 A274560

Adjacent sequences:  A265197 A265198 A265199 * A265201 A265202 A265203

KEYWORD

nonn,more

AUTHOR

Robert Price, Dec 04 2015

STATUS

approved

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Last modified May 26 13:59 EDT 2022. Contains 354092 sequences. (Running on oeis4.)